The present invention relates to a disk drive system for drive of a disk-shaped recording medium such as an optical disk or a magneto-optical disk.
A disk drive system includes a biaxial mechanism for controlling a tracking state of a light spot by driving an objective lens of an optical head on the basis of a tracking error signal obtained from track guide information on a pit train, a groove, and the like, and also includes a slide mechanism for displacing a relative position of the entire optical head to a disk plane in the radial direction of a disk.
As the slide mechanism, there are known a type of moving the entire optical head relative to a disk, and a type of moving a turn table on which a disk is mounted relative to an optical head whose position is fixed.
For a CD system, there is frequently adopted a type of sliding an optical head by a moving mechanism such as a gear system or a linear motor, which is generally called xe2x80x9ca thread mechanismxe2x80x9d. The thread mechanism includes a servo-loop for driving the thread mechanism in accordance with error information.
One example of a thread servo will be described with reference to FIG. 1.
A disk 1, while being rotated by a spindle motor 61, is irradiated with a laser beam emitted from an optical head 62 for recording or reproducing data in or from the disk 1. Information composed of light reflected from the disk 1 is detected and is then supplied to a RF amplifier 64.
The RF amplifier 64 converts the reflected light information (or a current signal corresponding to light quantity) into a voltage value, and also performs a matrix calculation of the reflected light information to extract, from the reflected light information, information necessary for a wide variety of servo operations as well as a reproducing operation.
With respect to a thread error signal used for a thread servo loop, there is known, for example, a method of producing a thread error signal by extracting a low frequency component from a tracking error signal used for a tracking servo through a low pass filter. This is because a thread error signal may be composed of a signal indicating the amount of offset between the entire optical head 62 and an objective lens driven for tracking by a biaxial mechanism in the optical head 62.
For example, in the thread servo shown in FIG. 1, a position error signal generating unit 65 receives a tracking error signal outputted from the RF amplifier 64, and extracts a low frequency component from the tracking error signal to generate a thread position error signal SLEp.
A position control signal generating unit 66 receives the thread position error signal SLEp from the position error signal generating unit 65, and generates a thread position control signal CSLp for driving the thread mechanism 63. The thread position control signal CSLp is converted, at a thread driver 67, into a thread drive signal SLD to be actually applied to a thread motor in the thread mechanism 63. The thread mechanism 63 is thus driven on the basis of the thread drive signal SLD, to move the optical head 62 to a specific position in the radial direction of the disk 1.
A tracking error signal shown in FIG. 2C is supplied to a low pass filter, to generate a thread position error signal SLEp shown in FIG. 2B. In addition, the thread position error signal SLEp shown in FIG. 2B, which is a low frequency component extracted from the tracking error signal through the low pass filter, has a phase delay relative to the tracking error signal.
The thread position error signal SLEp indicates an irradiation angle of a laser beam emitted from the optical head 62 relative to the disk plane. To adjust such an irradiation angle at a right angle, the slide mechanism 63 slides the optical head 62 in the direction in which the thread position error signal SLEp becomes zero.
For this purpose, the position control signal generating unit 66 outputs the thread position control signal CSLp shown in FIG. 2A on the basis of the thread position error signal SLEp. The thread drive signal SLD is generated on the basis of the thread position control signal CSLp.
Such a thread servo, however, has a problem that thread movement is liable to be made unstable, and is thereby frequently out of control, leading to a runaway state.
In the case where thread driving is performed on the basis of the thread position control signal CSLp generated from the thread position error signal SLEp, the thread driving should be theoretically performed depending on the thread position error signal SLEp even if such a thread position error signal SLEp is a significantly small value; however, since there exists a dead zone of about 1 V in the thread system, the thread mechanism 63 cannot be actually driven unless the thread drive signal SLD exceeds the dead zone voltage.
The dead zone voltage cannot be specified, and accordingly a voltage being considered to be sufficiently larger than the dead zone voltage is actually required to be applied.
As is apparent from the signal waveform example shown in FIG. 2C, with respect to a level of the tracking error signal, peak positions in the height direction in the figure are varied. This is because the peak positions of the tracking error signal is made unstable by an effect of the dead zone (dead zone voltage varied depending on electrical and mechanical characteristics of the thread system and the drive mechanism and also the thread position).
The effect of the dead zone actually makes it difficult to control linearly even a linear drive system and to make unstable operation of the linear drive system.
In the thread position control, runaway may most easily occur at the time of thread-on because a control target value is abruptly set at a position different from the present thread position.
FIG. 3 shows one example of a step response in position control.
As shown in this figure, when the thread mechanism is driven from the time of thread-on to a specific converged value, there frequently occurs an over-shoot or ringing indicated by a broken line because of a phase delay of the control loop. That is, the thread mechanism is out of control, to thus enter in a runaway state.
To realize a stable thread servo by solving the above-described runaway, there may be considered a thread servo shown in FIG. 4.
The thread servo shown in FIG. 4 has a velocity sensor 68 for detecting a moving velocity of the thread mechanism 63. Thus, the thread position error signal SLEp and velocity information from the velocity sensor 68 are supplied to a circuit unit as a velocity control signal generating unit 69.
The velocity control signal generating unit 69 sets a target velocity corresponding to a movement amount to a target position on the basis of the thread position error signal SLEp, and obtains a thread velocity error from a difference between the target velocity and the present velocity.
The velocity control signal generating unit 69 generates a thread velocity control signal CSLv corresponding to the thread velocity error signal, and supplies it to a thread driver 67.
In other words, the thread servo has a double loop configuration of a loop depending on a position error and a loop depending on a velocity error, in which the velocity error becomes zero when the position error becomes zero and such a point becomes a converged point.
With the thread servo having the double loop configuration depending on a position error and a velocity error, thread operation is controlled even in terms of its velocity, to prevent runaway, thus stabilizing the thread servo.
The above-described thread servo, however, has a problem. To obtain velocity information, the thread servo adopts a thread mechanism using a velocity sensor having a linear motor, or in the case where the thread servo adopts a thread mechanism using a gear system, the thread mechanism requires a double-phase sensor and a velocity signal generating circuit. As a result, the thread servo requires expensive parts and is complicated in its mechanism and its circuit configuration.
An object of the present invention is to provide a disk drive system including a thread servo having a simple and inexpensive configuration and being capable of preventing an unstable operation.
To achieve the above object, according to the present invention, there is provided a disk drive system including: a slide servo means for receiving an error signal of said slide mechanism and generating a slide drive signal on the basis of the error signal, thereby driving said slide mechanism; and a drive releasing means for detecting a precursory phenomenon of making unstable operation of said slide mechanism, and stopping a driving operation of said slide mechanism by said slide servo means upon detection of the precursory phenomenon.
A state in which the possibility of occurrence of runaway due to an over-shoot or ringing is high can be detected by monitoring a thread moving state or the like, and when such a state is detected, the drive releasing means stops the driving operation of the slide mechanism by the slide servo means for allowing the thread mechanism to run only by its inertia force, thereby avoiding occurrence of runaway. And, after an elapse of a specific time, the driving operation of the slide mechanism by the slide servo means is started again, so that the slide mechanism can be stably converged.